Gamma-ray Large Area Space Telescope

1. Gamma-ray Large Area Space Telescope OSU and GLAST Richard E. Hughes,The Ohio State University,The GLAST-LAT Collaboration. Department of Energy Review 28-Sep-2006

2. What is GLAST? Gamma-ray Large Area Space Telescope Two GLAST instruments: LAT: 20 MeV – >300 GeV GBM: 10 keV – 25 MeV Launch: 2007 GLAST Large Area Telescope (LAT) GLAST will map the universe in gamma rays Burst Monitor (GBM)

3. GLAST LAT Collaboration United States • California State University at Sonoma • University of California at Santa Cruz - Santa Cruz Institute of Particle Physics • Goddard Space Flight Center – Laboratory for High Energy Astrophysics • Naval Research Laboratory • The Ohio State University • Stanford University (SLAC and HEPL/Physics) • University of Washington • Washington University, St. Louis France • IN2P3, CEA/Saclay Italy • INFN, ASI Japanese GLAST Collaboration • Hiroshima University • ISAS, RIKEN Swedish GLAST Collaboration • Royal Institute of Technology (KTH) • Stockholm University PI: Peter Michelson(Stanford & SLAC) ~225 Members (including ~80 Affiliated Scientists, plus 23 Postdocs, and 32 Graduate Students) Cooperation between NASA and DOE, with key international contributions from France, Italy, Japan and Sweden. Managed at Stanford Linear Accelerator Center (SLAC).

4. Simulated LAT (>100 MeV, 1 yr) Simulated LAT (>1 GeV, 1 yr) EGRET (>100 MeV) The Gamma-Ray Sky • Comparing EGRET to GLAST: • Illustrating the anticipated improvement in our knowledge of the sky

5. Opacity (Salamon & Stecker, 1998) opaque No significant attenuation below ~10 GeV. Why study g’s? only e-tof the original source flux reaches us Gamma rays: • Source: • g rays do not interact much at their source: they offer a direct view into Nature’s largest accelerators. • the Universe is mainly transparent to g rays: can probe cosmological volumes. Any opacity is energy-dependent. • g rays are neutral: no complications due to magnetic fields. Point directly back to sources, etc. • Detection: • g rays readily interact • Very clear signature. • Good probe for new physics! • Decays of possible dark matter particles • Tests of fundamental physics (lorentz invariance, etc) GLAST Large Area Telescope (LAT) Burst Monitor (GBM)

6. GLAST Science GLAST will have a very broad menu that includes: • Systems with supermassive black holes • Gamma-ray bursts (GRBs) • Pulsars • Solar physics • Origin of Cosmic Rays • Probing the era of galaxy formation • Discovery! Particle Dark Matter? Hawking radiation from primordial black holes? Other relics from the Big Bang? Testing Lorentz invariance. New source classes. Huge increment in capabilities. GLAST draws the interest of both the the High Energy Particle Physics and High Energy Astrophysics communities.

7.  e– e+ GLAST LAT Overview: Overall Design • Anticoincidence Detector: • Highly efficient segmented scintillator tiles • First step in reduction of large charged cosmic ray background • Segmentation reduces self veto at high energy • Overall LAT Design: • 4x4 array of identical towers • 3000 kg, 650 W (allocation) • 1.8 m  1.8 m  1.0 m • 20 MeV – >300 GeV • Thermal Blanket: • And micro-meteorite shield • Precision Si-strip Tracker: • Detectors and converters arranged in 18 x-y tracking planes • Measures incident gamma direction • Hodoscopic CsI Calorimeter: • Segmented array of CsI crystals • Measures the incident gamma energy • Rejects cosmic ray backgrounds • Electronics System: • Includes flexible, highly-efficient, multi-level trigger

8. Cosmic Rays in the LAT: The Movie Muons taken during Integration and Testing with the full LAT

9. 2005-6 OSU Contributions to GLAST • DAQ Testing (Winer) • Code Development (EbfWriter package) • Using GLEAM (GLAST Gen/Sim) to create data sample • Timing Synchronization and Stress Test (e.g. DAQ rates) • Spacecraft Information data stream • Filtering (Hughes,Sander,Smith) • Port of Onboard Filter to Ground Software environment • Development of Filter for Calorimeter Calibration • Development of Filter for Tracker Alignment • Flight software development • Onboard Science (Kuehn, Smith, Hughes, Winer) • GRB Identification Algorithm • Ground Science • New physics: Tests of Lorentz Invariance (Kuehn) • Search for Dark Matter (Sander)

10. Digis DAQ/TriggerTestbed:FES Input EbfWriter TDS Code from Flight Software OnBoardFilter TDS FilterAlg/Other Producing Data for the TestBed • EbfWriter: Software package designed to format data from GLEAM exactly like the satellite would. • ALSO: produces data files needed by the TestBed Work By Winer/Hughes

11. DAQ/Trigger Testbed Tests VxWorks Nodes GLEAM/EbfWriter CAL/TKR/ACDFiles DAQ/TriggerTestbead FrontEnd Simulators (FES) Samples : Single Particle AllGamma Sample Background Sample Data Challenge 1 Integrity TestingRate TestingFilter Testing SoftwareEvent TEMs Compare Predicted vs Observed GASU HardwareEvent OnBoardFilter Work by Brian Winer

12. Front-end Simulator Front-end Simulator (FES) Board • System uses 9 PC’s • 8 PC’s for 16 TEM’s • 1 PC for ACD • Data transported to towers via high-speed data link; PCI bridge to local bus on simulator • Data Simulators interface to TEM like CAL and TKR sub-system electronics • CAL and TKR simulator board identical except code in FPGA’s • Can operate TEM or LAT with data generated from simulations

13. TestBed at SLAC TEMs GASU Racks with PCs for driving FES boards.

14. Example result from Testbed Runs Generated 4.5 Million backgroundevents for running through thetestbed. * Check DAQ system for data corruption. * Measure expected deadtime in DAQ system. Deadtime was found to be a few percent as expected. Black Points: Data captured at the output of the testbed. Red Hist: Expected output predicted by detector sim. Green: Ratio of black points and red histograms…all at 1.0 Work By Brian Winer

15. Level 1 Hardware Triggers (Did anything happen?) Example of photon LAT, producing e+/e- pair, triggering a Tkr 3-in-a-row and depositing energy in certain CAL crystals • Tkr 3-in-a-row • 3 x,y planes hit in a row • “workhorse” γ- ray trigger • CAL-LO • any log with >100MeV • CAL-HI • > 0 crystals with > 1GeV • indicates a high energy event • CNO • ACD hit with high discriminator signal • Throttle • a tower with a Tkr 3-in-a-row is • shadowed by an ACD hit Upon L1trigger: all towers read out within 20s L1 trigger rate ~ <3kHz> Combinations of these trigger primitives are used to define a hardware trigger

16. GLAST Data Rates and OnboardFilter • Downlink rate: 1.2Mbps • Average event size ~3kb (after compression) • Accept rate must be < 400 Hz • Expected background rate after triggering: ~3-4 kHz • CREME96 model (used by NASA, DepDef, commercial satellites) • Contains CNO, albedo, electrons, etc • Hardware trigger vetoes reduce rate by ~30% • Search for cosmics by shadowing of towers by ACD tiles • Reduces “good” gammas by ~3% • Still need to reduce rate by ~factor of 10 • Use software filter: OnboardFilter

17. The OnboardFilter • The onboard filter is software written in C • Runs on the EPU • Purpose • GammaFilter: Reduce overall rate to <400Hz • CNO Filter: Select events for calorimeter calibration • AlignmentFilter: Select events for aligning the tracker • OnboardScience: Not strictly part of the filter. Needed to identify specific event types: e.g. GRBs Portion of the Filter Algorithm

18. Non  Background Composition How well does the onboard filter reject the background? Hardware Trigger After Onboard Filter Counts (Hz) Total Rate ~2600 Hz Total Rate ~370 Hz

19. Arbitrary Units Black: Gamma Red: Background Log10(Energy) MeV Efficiency of the Onboard Filter when the LAT has triggered

20. CNO Filter:Energy Calibration Work by OSU Student Patrick Smith • Use MIPs to calibrate CAL • MIPs leave a characteristic amount of energy in each layer • MIPs do not shower • We know the real energy of each peak which allows us to convert signal into the real energy Before CNO filter After CNO filter counts counts carbon peak carbon peak MeV MeV

21. Tracker alignment filterFor intra-tower alignment Work By OSU Student Aaron Sander Use MIP protons passing through 2 towers to find relative alignment of towers

22. Gamma Ray Bursts • Extemely bright objects, with very large power output, lasting anywhere from seconds to hours • discovered in 1967 by the Vela military satellites, searching for gamma-ray transients • Right: Hubble images of GRB 050709 • Detected by HETE • Chandra and Swift observed X-ray afterglow • Hubble observed optical afterglow (5,10, 19, 35 days after burst) • Short vs long bursts: • Short: Merging binaries? • Long: massive star collapsing to black hole?

23. Onboard Science The GRB finding Algorithm • GRB finding algorithms traditionally use temporal information to trigger • The LAT’s good pointing ability allows for the use of spatial information in the trigger • The algorithm looks for a “large” (improbable) number of photons in a short period of time, in a small region of the sky • We are beginning the implementation of the algorithm into the onboard environment now

24. Triggers & Probabilities Example spatial probability plot Background photon have “clusters” with low cumulative probability Work by OSU Student Fred Kuehn GRB photons have “clusters” with high cumulative probability A similar plot exists for the cumulative time probability (we will likely trigger on the sum of both)

25. Improving the Onboard Localization Work by OSU Student Patrick Smith

26. LAT will open a wide window on the study of the high energy behavior of bursts. GRBs and Instrument Deadtime Distribution for the 20 brightest bursts in a year (Norris et al) Time between consecutive arriving photons EGRET deadtime: ~100ms

27. Using GRBs as a Probe for New Physics Measuring GRB at different redshift can be used as a probe for Lorentz Invariance Violation • Effects arise in some Quantum Gravity Models. • Look for delayed arrival of photons as a function of energy. Credit: F. Longo; GLAST GRB Science Team

28. Raw calorimeter energy (log10(MeV)) Dispersion due to QG. Time between successive photons (s) Using GRBs as a Probe for New Physics • LAT provides a means to measure the high energy photons and arrival. • System clock: 50 ns • Other observations required to localize and measure redshifts. 20 bright GRBs @1 Gpc w/ QG. Norris, Bonnell, Marani, Scargle 1999 Work by OSU Student Fred Kuehn

29. Sensitivity • ∆E : the lever arm • for the instrument (Instrumental limit) • for the observed energies (Observing a source) • t : the time resolution • the time resolution of the instrument (Instrumental limit) • the binning time to have enough statistics (Observing a source) • L: the typical distance of the sources • If the instrument doesn’t see any delay: Eqg > (L·∆E)/(c·  t) • If I can see a delay ∂t : Eqg = (L·∆E)/(c·  t)

30. Particle Dark Matter Some important models in particle physics could also solve the dark matter problem in astrophysics. If correct, these new particle interactions could produce an anomalous flux of gamma rays. X q or gg or Zg q “lines”? X Just an example of what might be waiting for us to find!

31. Search For Dark Matter • Sources are easy to subtract • There is a diffuse background not attributed to particular point sources • To see photons from dark matter it is critical to properly model this diffuse component • OSU has started to contribute to modeling of diffuse via GALPROP • Large number of parameters • 1 run takes ~6h on 2GHz machine • The lines are: • DC data (yellow) • GP_gamma generated from galprop (blue) • catalogue sources (pink) • extragalatic background in (dark pink). Work By OSU Student Aaron Sander

32. Improving On-ground Analysis Tools Attempt at matching signal/background of standard… eventually improve upon Standard tool is classification Tree Work by OSU Undergraduate Lindsey Perry

33. Remaining Major Milestones LAT final assembly complete! Delivery of LAT to NRL for environmental testing (shake/temp tests): May 2006 GLAST integration with spacecraft and testing: Fall 2006 through Summer 2007 Launch: Oct/Nov 2007, Kennedy Space Center Begin science: 1-2 months after launch Lifetime of mission: at least 5 years (goal: 10 yrs) Launch of Spitzer Space Telescope on a Delta II - Heavy

34. Summary • OSU has made major contributions to GLAST over the past year • OSU is the lead group for the development of algorithms for: • Calibrations • Onboard Science • As well as subsequent Testing of these algorithms on the testbed • We have begun to transition to preparing to do the science • High profile topics: GRBs, New Physics, Search for Dark Matter